Excitatory and inhibitory actions of norepinephrine on the Ba2+ current through L-type Ca2+ channels of smooth muscle cells of guinea-pig vas deferens
✍ Scribed by N. Kamimura; S. Suga; J. Wada; Y. Mio; T. Suzuki; M. Wakui
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Volume
- 169
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
The effect of norepinephrine (NE) was examined on the whole-cell Ba2+ current through L-type Ca2+ channels of freshly isolated smooth muscle cells of guineapig vas deferens. The magnitude of maximum Ba2+ current [IBa(max)] varied in different cells, although the capacitance of the cell membrane was similar (-50 pF). Application of dbcAMP augmented IBa(max) by 37%, which was canceled by Rp-CAMPS, while PMA decreased the current by 32%, which was canceled by staurosporine. NE increased IBahax) of the cells which originally showed relatively small IBahax), and decreased the current of the cells which showed larger IBa(max). In the presence of phentolamine, NE increased IBa(max), and this effect was remarkable in cells showed smaller IBa(max). In the presence of propranolol, NE decreased IBa(max). The excitatory P-adrenoceptor activation was canceled by Rp-CAMPS, and the inhibitory a-adrenoceptor effect was canceled by staurosporine. It is suggested that NE shows dual (excitatory and inhibitory) actions on the L-type Ca2+ channels of smooth muscle of guinea-pig vas deferens. The excitatory P-adrenoceptor action mediated through cAMPIPKA is predominant in cells with lower density of the Ca2+ channels, while inhibitory a-adrenoceptor action mediated through PKC is predominant in cells with higher channel density.