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Monday 01 December 2003

The role of calcium channels in substance P-induced contractile response in the rat iris.

By: Grumann Junior A, Alves RV, Calixto JB.

Peptides 2003 Dec;24(12):1985-91

This study was undertaken to assess the role of calcium channels in the contractile response induced by substance P in the isolated rat iris. Substance P produced graded and sustained contraction in the rat iris. Pre-incubation of preparations with thapsigargin (1 microM), verapamil (1 microM), isradipine (1 microM) or with omega-conotoxin MCIIA (0.1 microM) did not significantly inhibit substance P-mediated contraction in the isolated rat iris. However, pre-incubation of the preparations with nicardipine (1 microM) or ruthenium red (1 mM) caused parallel displacement to the right of the substance P concentration-response curve without affecting its maximal response. In contrast, amiloride (1 microM), markedly inhibited substance P-mediated contraction (73 +/- 5%), while econazole (1 mM) also significantly inhibited (44 +/- 11%) substance P-mediated contraction in the isolated rat iris. Collectively, these results suggest that substance P-mediated contractile response in the isolated rat iris depends largely on the influx of external Ca2+, by a mechanism which might involve the T-type calcium channels.

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