Permissive Modulation of Sphingosine-1-Phosphate-Enhanced Intracellular Calcium on BKCa Channel of Chromaffin Cells

Abstract

Sphingosine-1-phosphate (S1P), is a signaling sphingolipid which acts as a bioactive lipid mediator. We assessed whether S1P had multiplex effects in regulating the large-conductance Ca2+-activated K+ channel (BKCa) in catecholamine-secreting chromaffin cells. Using multiple patch-clamp modes, Ca2+ imaging, and computational modeling, we evaluated the effects of S1P on the Ca2+-activated K+ currents (IK(Ca)) in bovine adrenal chromaffin cells and in a pheochromocytoma cell line (PC12). In outside-out patches, the open probability of BKCa channel was reduced with a mean-closed time increment, but without a conductance change in response to a low-concentration S1P (1 µM). The intracellular Ca2+ concentration (Cai) was elevated in response to a high-dose (10 µM) but not low-dose of S1P. The single-channel activity of BKCa was also enhanced by S1P (10 µM) in the cell-attached recording of chromaffin cells. In the whole-cell voltage-clamp, a low-dose S1P (1 µM) suppressed IK(Ca), whereas a high-dose S1P (10 µM) produced a biphasic response in the amplitude of IK(Ca), i.e., an initial decrease followed by a sustained increase. The S1P-induced IK(Ca) enhancement was abolished by BAPTA. Current-clamp studies showed that S1P (1 µM) increased the action potential (AP) firing. Simulation data revealed that the decreased BKCa conductance leads to increased AP firings in a modeling chromaffin cell. Over a similar dosage range, S1P (1 µM) inhibited IK(Ca) and the permissive role of S1P on the BKCa activity was also effectively observed in the PC12 cell system. The S1P-mediated IK(Ca) stimulation may result from the elevated Cai, whereas the inhibition of BKCa activity by S1P appears to be direct. By the differentiated tailoring BKCa channel function, S1P can modulate stimulus-secretion coupling in chromaffin cells.