Electrophysiological properties of different cell types in the shark rectal gland.
Electrophysiological properties of different cell types were studied in single rectal gland cells of Squalus acanthias by the whole-cell voltage clamp technique. Based on electrophysiological characteristics and primary morphological observations (light microscope, X400), three cell types (named as I, II, and III) were found in isolated fresh cells and two cell types (I and II) in primary cultured cells of the shark rectal gland (SRG). Type I cells had both Cl- (I(Cl)) and the inwardly rectifying K+ channel (I(K1)). Type II and III cells only had I(Cl) Under X400 light microscope granular materials in the cytoplasm were found in Type I and II cells, but not in Type III cells. The data from this study show that 65 % of isolated fresh SRG cells strongly expressed the K+ channel with much less amount of the Cl- channel and 35% had only I(Cl). In sharp contrast, 11% had I(K1) and I(Cl), and 89% had only I(Cl) in cultured SRG cells. Extracellular application of 10 microM forskolin significantly enhanced I(Cl) in primary cultured SRG cells. This enhancement was influenced by intracellular Ca2+ and blocked by 50 microM Ni2+. Other compounds, such as vasoactive intestinal peptide (VIP) and 8-(4-chlorophenylthio)-adenosine3':5'-cyclic monophosphate (cpt-cAMP) also enhanced I(Cl). Interestingly, cAMP and forskolin significantly inhibited I(K1) in cultured and fresh SRG cells. I(K1) was blocked by micromolar concentrations of Ba2+ and significantly altered by extracellular K+ concentrations. The present data suggest that 1) the shark rectal gland contains different cell types which may play various roles in the process of salt secretion; 2) I(Cl) and I(K1) in SRG cells are strongly modulated by cAMP, forskolin, and VIP, as well as Ca2+, K+, and Na+ ions.
Xiao
Y F
YF
Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA. yxiao@bih.harvard.edu
D000818:Animals; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004284:Dogfish; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D008564:Membrane Potentials; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D012491:Salt Gland / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D002614:Chelating Agents; D018118:Chloride Channels; D015221:Potassium Channels; D005576:Colforsin; D014660:Vasoactive Intestinal Peptide; D004533:Egtazic Acid; D000242:Cyclic AMP