On the transduction mechanism for muscarine‐induced inhibition of M‐current in cultured rat sympathetic neurones.

Abstract

SUMMARY1. Dissociated adult or fetal rat superior cervical ganglion cells were voltageclamped through a single patch pipette. The voltage-dependent K+ current, IM (Mcurrent), was maintained by including MgATP in the pipette solution and by buffering the solution pH to 6 7.2. Bath-applied muscarine (0 4 /IM) produced a reversible inhibition of IM.3. Addition of Gpp(NH)p (200 /tM) or GTP-y-S (500 /tM) to the pipette solution induced a slowly developing inhibition ofIM and prevented recovery from subsequent muscarine-induced inhibition.4. Addition of GDP-,/-S (500 uM) to the pipette solution reduced the amount of IM inhibition produced by 04 ,aM-muscarine by 42 % and reduced the associated inward shift of the holding current by 56 %.5. Cells responded normally to muscarine after pre-treatment for 4-27 h with 500 ng ml-1 pertussis toxin (PTx).6. IM was not diminished by extracellular addition of 1 mM-dibutyryl cyclic AMP, 8-bromo-cyclic AMP or dibutyryl cyclic GMP, or of 10 ,uM-forskolin.7. IM was not reduced by inclusion of Li' (2 mM) or inositol 1,4,5-trisphosphate (IP3, 100 /iM) in the patch pipette, nor by ionophoretic injection of 1P3 from an inserted micropipette.8. Addition of 4-,l-phorbol 12,13-dibutyrate (PDBu, 0 5-2 ,UM) to the extracellular medium partly inhibited IM and reduced an additional component of resting membrane current. This effect was not replicated by 4-a-phorbol 12,13-didecanoate. 9. It is concluded that the inhibition of IM by muscarine is mediated through activation of a PTx-insensitive GTP-binding protein. The effect of muscarine appears not to be mediated by cyclic nucleotides or 1P3 but may possibly involve the generation of diacylglycerols and activation of protein kinase C.

Bradykinin inhibits a potassium M‐like current in rat pheochromocytoma PC12 cells

“…Vehicle alone (0.01 °/0 ethanol) or the inactive 4-ct-12, 13 phorboldidecanoate (1 #M) had little or no effect on IM (n=5). These effects were comparable to those reported in frog [10,12], rat superior cervical ganglia [7] and NG108-15 cells [2]. The differences between PDBu and BK actions, together with the findings in frog neurons employing PKC inhibitors [12] make it unlikely that PKC plays a primary role in BK-induced IM inhibition.…”

“…Correspondence address: A. Villarroel, Howard Hughes Medical Institute, Department of Neurobiology and Behavior, SUNY at Stony Brook, Stony Brook, NY 11794-5230, USA demonstrated to be coupled via a pertussis toxininsensitive G protein by several laboratories [6][7][8]. Roles for protein kinase C (PKC) and inositol 1,4,5-trisphosphate (IP3) have been suggested in NG108-15 cells [2] and in rat hippocampal cells [9], respectively, although it has been argued that neither IP3 [10,11], nor PKC [12] mediate Ira inhibition in frog sympathetic ganglion cells.…”

Does diacylglycerol regulate KCNQ channels?

“…The possibility of roles for PKC remains a more difficult question. From work on frog neurons and frog smooth muscle, several investigators proposed that PKC might mediate muscarinic suppression of M current [12][13][14]. A strong reduction of current by OAG and PMA in C. elegans KCNQ homologs (KQT channels) expressed in Xenopus has also been attributed to activation of PKC, and, of the mammalian channels, KCNQ5 was shown to be strongly affected by PKC and the others not [25].…”

“…There is precedent for sensitivity to DAG. Older studies reported that activation of protein kinase C (PKC) by DAGs and phorbol esters can reduce M current [11][12][13][14], and newer papers suggest that KCNQ channels exist in a complex with bound PKC and can be phosphorylated [15]. In addition, some other ion channels are thought to be directly responsive to DAG independent of PKC [16][17][18].…”

Osmoregulatory inositol transporter SMIT1 modulates electrical activity by adjusting PI(4,5)P2levels

“…We tested the effect of myoinositol supplementation on electrical properties of primary cultured neurons. The superior cervical ganglion (SCG) neuron has been used as a model to study native KCNQ2/3 channels, which serve as a damper on their excitability (37,38). Neurotransmitters and drugs that close these channels remove the brake so the neurons fire more easily.…”