Determinants of the voltage dependence of G protein modulation within calcium channel beta subunits.

CaVbeta subunits of voltage-gated calcium channels contain two conserved domains, a src-homology-3 (SH3) domain and a guanylate kinase-like (GK) domain with an intervening HOOK domain. We have shown in a previous study that, although Gbetagamma-mediated inhibitory modulation of CaV2.2 channels did not require the interaction of a CaVbeta subunit with the CaValpha1 subunit, when such interaction was prevented by a mutation in the alpha1 subunit, G protein modulation could not be removed by a large depolarization and showed voltage-independent properties (Leroy et al.

Muscarinic receptor-activated cationic channels in murine ileal myocytes.

Background And Purpose: There is little information about the excitatory cholinergic mechanisms of mouse small intestine although this model is important for gene knock-out studies.

Experimental Approach: Using patch-clamp techniques, voltage-dependent and pharmacological properties of carbachol- or intracellular GTPgammaS-activated cationic channels in mouse ileal myocytes were investigated.

Key Results: Three types of cation channels were identified in outside-out patches (17, 70 and 140 pS).

[Single nonselective cation channels activated by muscarinic agonists in smooth muscle cells of the guinea-pig small intestine].

The carbachol-evoked inward cationic current in guinea-pig ileum smooth muscle cells is comprised of three types nonselective cationic channels (NSCC) with small (10 +/- 2 pS), medium (56 +/- 8pS) and large (135 +/- 14 pS) unitary conductance. All three types of NSCC could be activated by external application of carbachol as well as by internal application of GTPgS. It was found that behavior of carbachol- and GTPgammaS-evoked whole-cell current is mainly determined by the properties of medium conductance channels.