Decay in Prepulse Facilitation of Calcium Channel Currents by Gi/o-Protein Attenuation in Hamster Submandibular Ganglion Neurons, But Not Gq/11.

Abstract

The calcium ion influx through voltage-dependent calcium channels (VDCCs) has a vital role in the control of neurotransmitter release and membrane excitability. Prepulse facilitation is a phenomenon in which a strong depolarizing pulse induces a form of the VDCCs that exhibits an increased opening probability in response to a given test potential; this persists for several seconds after repolarization. It has been reported that prepulse facilitation occurs via dissociation of the guanosine triphosphate (GTP)-binding proteins (G-proteins) from the VDCCs and that recovery from facilitation involves rebinding of the G-proteins.The heterotrimeric G-proteins act as switches that regulate information processing circuits connecting cell surface G-protein-coupled-receptors to a variety of effectors. In this study, we have studied the characterization of G-protein subtypes in prepulse facilitation of VDCCs currents (I Ca ) in hamster submandibular ganglion (SMG) neurons, using whole-cell patch clamp recordings.Under control conditions, with GTP (0.1mM) in the recording pipette, the rate of prepulse facilitation was ‫%9.1ע0.91‬ (n‫.)31ס‬ Intracellular dialysis with GDP-␤-S (0.1mM), G-protein blocker, and pretreatment of neurons with N-ethylmaleimide (NEM) (100M for 2min), G i/o blocker, attenuated the rate of prepulse facilitation. Intracellular dialysis of anti-G q/11 -antibody did not alter it. These results suggest that prepulse facilitation of VDCCs is due to G i/o -types of G-protein, but not to the G q/11 -type, in SMG neurons.

A Central Role of Connexin 43 in Hypoxic Preconditioning

“…The conductance of the slowly gating state was 15 Ϯ 0.5 pS (Table 1, ␥ sub ). The conductance of Cx43 hemichannel openings was smaller than observed previously using whole-cell recordings (Endoh et al, 2001;Contreras et al, 2003) and may reflect that the opening state of Cx43 channels is sensitive to the recordings conditions. A possible explanation is that loss of cytosolic components modulate the gating properties of Cx43 hemichannels similar to other channels (Donevan and Rogawski, 1995).…”