抄録
In the ciliary muscle, muscarinic stimulation evokes an inward current which probably results from opening of non-selective cation channels (NSCCs). They may possibly serve as routes of Ca2+ influx required for sustained contraction of this smooth muscle that lacks voltage-gated Ca2+ channels. We examined here the properties of the NSCCs by current-noise analysis in the porcine ciliary muscle.
METHODS Whole-cell membrane currents were recorded by voltage clamp in porcine ciliary myocytes freshly dispersed with collagenase. The bath was perfused with a physiological saline buffered with 10 mM-HEPES. Pipettes were filled with a K+-free solution containing 100 mM Cs aspartate, 5 mM-BAPTA ([Ca2+]=70 nM) and 200 μM-GTP (pH 7.0). Experiments were carried out at 30°C. For RT-PCR, specific primers for TRPC homologues were designed on the basis of cDNA sequences reported for several mammalian species.
RESULTS & DISCUSSION Under voltage clamp at -50 mV, CCh (2 μM) evoked inward currents accompanied by a marked increase in noise. The plot of variance against mean of the current exhibited two linear components, indicating the existence of two types of NSCCs with unitary conductances of 35 pS and 95 fS. FFT analysis of the noise gave power spectra to which a double-Lorentzian function was fitted with corner frequencies of 14 ± 3 and 82 ± 5 Hz (n=35). RT-PCR identified high level of mRNA of several TRPC homologues which have been shown to constitute NSCCs modulated by G-protein-linked mechanisms. [Jpn J Physiol 54 Suppl:S137 (2004)]
