1 11 3 Aquatic Osmoregulation BIO 361T Fall 2014 1 Marine Challenge In a hyperosmotic environment maintain low NaCl levels In the figure of the chloride cells below label the apical and basolateral sides Use each piece in the Channel Bank once to drive Na and Cl into the water Draw each channel in its respective position Label each channel and specify which direction each solute is moving and whether it requires ATP Channel Bank Na Cl K symporter K channel Na K ATPase uses ATP to exchange 3 Na for 2 K Cl channel 2 How does the Na K ATPase drive Na excretion from the cells into the water Pumps Na into the ECF so it can leak paracellularly down its chemical gradient 3 How do the Na K ATPase and symporter work together to drive Cl into the water Pumps Na into the ECF which goes down its chemical gradient into the cell and takes Cl with it which leaves via a Cl channel into the water 4 What would happen to NaCl in the ECF if it were not osmo and ionoregulated using these mechanisms It would increase either because it would enter passively from the water or because H2O would leave the body for the more hyperosmotic seawater 2 5 Freshwater Challenge 1 In a hypoosmotic environment maintain high Na levels In the figure of the PNA chloride cells below label the apical and basolateral sides Use each piece in the Channel Bank once to drive Na in from the water Draw each channel in its respective position Label each channel and specify which direction each solute is moving and whether it requires ATP Channel Bank H ATPase uses ATP to pump protons Na channel Na K ATPase uses ATP to exchange 3 Na for 2 K Cl HCO3 exchanger Focus on role of generating an electrical gradient 6 How does the Na K ATPase drive Na movement into the body from the water Keeps intracellular Na low creating a concentration gradient 7 Is the Na channel responsible for active or passive movement List two reasons that support your answer Passive It does not use ATP and it only allows Na to follow its electrochemical gradient 8 How does the H ATPase contribute to Na movement into the body from the water Keeps inside of cell less positive creating an electrical gradient 9 Why do you think the PNA chloride cells are important in helping the fish deal with acidosis Can upregulate the apical H ATPase to offload protons raising internal pH to normal levels 3 10 What is the role of carbonic anhydrase in these cells and how is this related to the Cl HCO3exchanger Converts CO2 and H2O into H and HCO3 providing H to be pumped out and create an electrical gradient Also provides HCO3 for the exchanger allowing Cl to be brought into the cell to make it even less positive 11 What is the importance of having tight junctions in freshwater gills Prevents ions and water from flowing between cells The concentration gradients established by the pumps are maintained and flow is diverted through the appropriate channels 12 Freshwater Challenge 2 In a hypoosmotic environment maintain high Cl levels In the figure of the PNA chloride cells below label the apical and basolateral sides Use each piece in the Channel Bank once to drive Cl in from the water Draw each channel in its respective position Label each channel and specify which direction each solute is moving and whether it requires ATP Channel Bank H ATPase Cl HCO3 exchanger Also basolateral Cl channel not shown 13 What is the role of carbonic anhydrase in these cells and how is this related to the Cl HCO3exchanger Converts CO2 and H2O into H and HCO3 providing HCO3 for the exchanger allowing Cl to be brought into the cell from the freshwater 14 How does the H ATPase contribute to Cl movement into the body from the water Drives the conversion of CO2 and H2O into H and HCO3 via carbonic anhydrase 4 15 What is the function of the rectal gland in elasmobranchs Increase excretion of Na and Cl by pumping Na out of tubular cells which make the cells more negative thus creating an electrical gradient that drives Cl out to the lumen Na diffuses paracellularly into the lumen These empty into the digestive tract to be excreted This allows sharks and rays to ionoregulate their ECF preventing them from being as high in NaCl as seawater 16 Forrest et al 1973 removed the rectal gland of the spiny dogfish RGEX and measured Na in the plasma over the course of eight days As a negative control they performed a fake operation on another group of dogfish SHAM and compared the two groups Do these data support your previous answer CHLORIDE TRANSPORT IN THE SHARK RECTAL GLAND51 519 PLASMA SODIUM RGEX 280 270E 260 SHAM 11 1 250 0 1 2 3 4 DAYS 5 6 7 8 FIG 3 Plasma sodium values of live Squalus acanihias after excision of the rectal gland or after a sham operation Sharks without rectal glands have progressively higher plasma Na because they are unable to excrete it The rectal gland is necessary to the economy of the shark When it is removed Fig 3 there is a progressive rise in serum sodium and chloride 3 The composition of rectal gland secretion consists almost entirely of hypertonic sodium chloride at approximately the concentration of seawater 11 2 to 2 times the concentration of salt in the shark plasma There are miniscule amounts of urea in the rectal gland secretion which is isotonic in osmotic terms with plasma An important feature of rectal gland secretion as observed in the artificially perfused gland is that the duct is always electrically negative to the perfusate Thus chloride appears to be moving against both a chemical and an electrical gradient into the duct of the gland Sodium on the other hand moves down an electrical gradient although against a chemical gradient 4 HORMONAL CONTROL OF RECTAL GLAND SECRETION Rectal gland secretion is under the control of cyclic AMP 5 The addition of either cAMP or theophylline to solutions perfusing the gland results in an enormous increase in secretory activity When secretion is stimulated in this way the electrical potential difference between duct and perfusate invariably becomes more negative and the concentration of sodium chloride in the secretion sometimes increases 4 Thus cyclic AMP stimulates the movement of chloride against an even higher electrochemical gradient than existed previously underlining the active nature of chloride transport in rectal gland secretion Control of biological activity by adenylcyclase the second messenger usually implies the existence of a hormonal first messenger The active polypeptide hormone in this case appears to be vasoactive
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