Activation of Ca2+-dependent Cl- and K+ conductances in rat and mouse parotid acinar cells.

Abstract

Isolated acinar cells from rat and mouse parotid glands were studied with patch-clamp whole-cell current recordings. Acetylcholine (ACh) stimulation caused a transient inward current at a membrane potential of -70 mV, and a sustained outward current at a membrane potential of 0 mV, in quasi physiological Nat, K+ ion gradients, except the zero-C1-ion gradient condition across the membrane. The reversal potential obtained from the ACh-evoked steady current was about -75 mV, in this ionic condition. When major Cl-ions of both the pipette and the bath solution were replaced, either by glutamate or by sulphate, only a large outward current was observed, at a membrane potential of -60 mV , in the presence of ACh. The addition of Cat+-ionophore A23187 caused responses similar to those evoked by ACh. The reversal potential of A23187-induced current was close to the K+ equilibrium potential of -90 mV, in a C1 -free condition. When K+-free NaCI solution was used in the pipette and the bath, A23187 caused only a large inward current, at a membrane potential of -60 mV. The reversal potential of A23187-evoked current was about -15 mV, in a symmetrical K+-free, NaCI condition. These results suggest that the ACh and A23187 activate Clr as well as K+ conducting pathways via an increase in [Ca2+]i in the parotid acinar cells. The A23187-evoked large K+ current could not be explained solely by a rise in open probability of the channels.

Physiological localization of an agonist-sensitive pool of Ca2+ in parotid acinar cells.

“…Taken together with previous data (6,(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28), these results indicate that a rise in [Ca2+], is in fact necessary to activate basolateral membrane K+ conductance. The blunted response of Me2BAPTA-loaded cells ( Fig.…”

“…(ii) the cellular K+ loss is abolished in Ca2+-depleted cells stimulated in Ca2+-free medium (22,23), (iii) the application of Ca2" ionophores to acinar cells activates K+ channels and causes a loss of cellular K+ similar to that caused by agonists (23)(24)(25)(26), (iv) the intracellular perfusion of a Ca2+ chelator blocks the agonist-stimulated increase in K+ conductance (18,26,27), and (v) the intracellular perfusion of inositol trisphosphate activates the K+ conductance (28).…”

Loss of Hyperpolarization-activated Cl− Current in Salivary Acinar Cells from Clcn2 Knockout Mice

“…Salivary gland acinar cells are no exception, expressing at least five distinct chloride conductances (18,19). The first of these to be characterized (20) is activated by an increase in intracellular free [Ca 2ϩ ] i (21). It is likely that the Ca 2ϩ -dependent Cl Ϫ channel is targeted to the apical membrane in parotid acinar cells as has been shown in pancreatic acinar cells (22).…”

SK4/IK1-like channels mediate TEA-insensitive, Ca2+-activated K+ currents in bovine parotid acinar cells

“…It has been suggested, however, by a number of other studies using whole cell patch-clamp techniques or K ϩ (and Rb ϩ ) efflux measurements that K Ca channels, distinct from maxi-K ϩ channels, may also contribute significantly to the outward K ϩ current in the acinar cells of various salivary glands including rat parotid (29,46), sheep parotid (20,55), bovine parotid (34), rat mandibular (26,27), and mouse mandibular glands (22). These studies have shown that a maxi-K ϩ channel blocker, TEA, is largely ineffective in inhibiting muscarinically or Ca 2ϩ -evoked K ϩ conductance.…”