Abstract
Effects of cAMP on Cl– secretion, intracellular Cl– activity and cell volume were studied in isolated perfused rectal gland tubules (RGT) of Squalus acanthias with electrophysiological and fluorescence methods. Recording of equivalent short-circuit current (I sc) showed that cAMP stimulates Na+Cl– secretion in a biphasic manner. The first and rapid phase corresponds to Cl– exit via the respective protein-kinase-A- (PKA-) phosphorylated Cl– conductance. The inhibitory effect of the loop diuretic furosemide (0.5 mmol/l, n=12) indicates that second phase reflects the delayed (1–2 min) activation of the Na+2Cl–K+ cotransporter. During the first phase cytosolic Cl– activity, as monitored by 6-methoxy-N-(3-sulfopropyl) quinolinium (SPQ) fluorescence, fell to 78% (n=23) of the control value. Concomitantly, a transient fall in cell volume was recorded by calcein fluorescence to 92% (n=5) of the control value. Preincubation of the RGT with phalloidin (0.1 mmol/l, n=6) or cytochalasin D (0.1 mmol/l, n=4) almost completely prevented the development of the second phase of I sc activation. When cytosolic Cl– activity was increased by exposing the RGT to a high K+ concentration (25 mmol/l), in the presence of mannitol to prevent volume increases, stimulation was unaffected and biphasic. In contrast, when cell volume was clamped to an increased value (115%, n=8) by removing extracellular NaCl, the second phase was abolished completely (n=11). These data suggest that the primary and key process for triggering the Na+2Cl–K+ cotransport is transient cell shrinkage.
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Received: 11 February 1999 / Accepted: 24 March 1999
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Greger, R., Heitzmann, D., Hug, M. et al. The Na+2Cl–K+ cotransporter in the rectal gland of Squalus acanthias is activated by cell shrinkage. Pflügers Arch 438, 165–176 (1999). https://doi.org/10.1007/s004240050895
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DOI: https://doi.org/10.1007/s004240050895