AJP - Cell Physiology, Vol 260, Issue 4 C824-C831, Copyright © 1991 by American Physiological Society
Cl- secretion by cultured shark rectal gland cells. II. Effects of forskolin on cellular electrophysiology
W. M. Moran and J. D. Valentich
Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225.
Employing microelectrode techniques we have assessed the cellular
electrophysiological properties of shark rectal gland (SRG) cells in
primary culture. In the absence of secretagogues a 10-fold reduction in the
Cl- concentration of the apical superfusate shark Ringer solution had
little effect on either apical membrane electrical potential difference
(Va) or fractional resistance (fRa), indicating little, if any, apical
membrane Cl- conductance. Superfusing the basolateral surface with high-K+
shark Ringer solution (K+ increased 10-fold) depolarized the basolateral
membrane electrical potential difference (Vb) by 43 mV, indicating that
this barrier is largely K+ conductive. In addition, basolateral Ba2+ (5 mM)
depolarized Vb by 12 mV and reduced fRa from 0.92 to 0.58, results
consistent with a K(+)-conductive basolateral membrane in unstimulated SRG
cells. Basolateral forskolin (10(-6) M) depolarized Va by 25 mV and caused
a dramatic reduction in fRa from 0.97 to approximately 0.10. Under these
conditions, a 10-fold decrease in apical superfusate Cl- concentration
depolarized Va by 37 mV, revealing an adenosine 3',5'-cyclic
monophosphate-induced apical membrane Cl- conductance. The time course of
the forskolin-induced changes in Va and Vb suggests that the basolateral
membrane K+ conductance increased and maintained the driving force for
apical Cl- exit, as in other Cl(-)-secreting epithelia. These
electrophysiological properties compare favorably with those of the
perfused SRG tubule and indicate that SRG primary cultures are a suitable
model for Cl(-)-secreting epithelia.
