Arachidonic acid both inhibits and enhances whole cell calcium currents in rat sympathetic neurons

Abstract

We recently reported that arachidonic acid (AA) inhibits L- and N-type Ca(2+) currents at positive test potentials in the presence of the dihydropyridine L-type Ca(2+) channel agonist (+)-202-791 in dissociated neonatal rat superior cervical ganglion neurons [Liu L and Rittenhouse AR. J Physiol (Lond) 525: 291-404, 2000]. In this first of two companion papers, we characterized the mechanism of inhibition by AA at the whole cell level. In the presence of either omega-conotoxin GVIA or nimodipine, AA decreased current amplitude, confirming that L- and N-type currents, respectively, were inhibited. AA-induced inhibition was concentration dependent and reversible with an albumin-containing wash solution, but appears independent of AA metabolism and G protein activity. In characterizing inhibition, an AA-induced enhancement of current amplitude was revealed that occurred primarily at negative test potentials. Cell dialysis with albumin minimized inhibition but had little effect on enhancement, suggesting that AA has distinct sites of action. We examined AA's actions on current kinetics and found that AA increased holding potential-dependent inactivation. AA also enhanced the rate of N-type current activation. These findings indicate that AA causes multiple changes in sympathetic Ca(2+) currents.

M1Muscarinic Receptors Inhibit L-type Ca2+Current and M-Current by Divergent Signal Transduction Cascades

“…To date, s/cPLA 2 Ϫ/Ϫ mice are known to differ biochemically from wild-type mice in one respect: they have decreased levels of cyclooxygenase-2 (COX-2) mRNA and protein (Bosetti and Weerasinghe, 2003). Decreased COX-2 in s/cPLA 2 Ϫ/Ϫ SCG neurons is unlikely to account for the loss of L-current inhibition because we found no evidence that AA metabolism is required for L-current inhibition (Liu et al, 2001;Liu and Rittenhouse, 2003). Thus, we propose a pathway in which M 1 R coupling to G q/11 activates breakdown of PIP 2 by PLC.…”

“…(1) AA mimics inhibition of L-channel activity by Oxo-M recorded in whole-cell and cell-attached patch configurations (Mathie et al, 1992;Rittenhouse, 2000, 2003;Liu et al, 2001). (2) The kinetics of Oxo-M-inhibited L-currents are statistically indistinguishable from those in the presence of AA.…”

“…1 B, D). Second, including the L-channel agonist FPL in the bath elicited a long-lasting tail current comprising entirely L-current (Liu et al, 2001). Under these conditions, reversible muscarinic inhibition of the long-lasting tail current occurred but was also lost with MT-7 (Fig.…”

“…Dissociated sympathetic neurons were obtained from SCG of 1-to 4-d-old Sprague Dawley rats (Charles River Laboratories, Wilmington, MA) following the methods of Liu and colleagues (Liu et al, 2001;Liu and Rittenhouse, 2003). Cells were incubated at least 4 h before initiating whole-cell recording experiments and used within 12 h to avoid recording from cells with processes.…”

Cholesterol Inhibits M-type K+ Channels via Protein Kinase C-dependent Phosphorylation in Sympathetic Neurons

“…Recently, lipid molecules have been found to act as signaling molecules (11)(12)(13). One of the most famous molecules in this respect is phosphatidylinositol 4,5-bisphosphate (PIP 2 ).…”