Non selective Ca2+ channels are involved in the contraction induced by NH4Cl in the rat anococcygeus muscle but not the Ca2+ voltage operated channels neither Ca2+ channels activated by protein Kinase‐C (PKC)

Changes in cytosolic Ca 2+ concentration ([Ca 2+ ]c) associated to the contraction are brought about by Ca 2+ influx and release from sarcoplasmic reticulum and pH can affect both processes. The aim of this study was to investigate Ca 2+ influx pathways that contribute to the contractile response induced by the alkalinizant agent NH 4 Cl, in rat anococcygeus smooth muscle. The muscle isometric tension was recorded on a polygraph, and [Ca 2+ ]c was measured on isolated cells loaded with 5 μM FURA2/AM by the ratio: 340/380 nm. [Ca 2+ ]c was increased by 10 mM NH 4 Cl (100%) when compared to 0.1 μM phenylephrine (57.0±12.3% n=4). Incubation for 1 min in Ca 2+ ‐free medium reduced the contractions induced by 10 mM NH 4 Cl to 11.5±5.1% (n=5) compared to the contractions induced in 2.5 mM Ca 2+ solution (100%). After 3 min in Ca 2+ free solution, the contractions stimulated with NH 4 Cl were almost abolished (0.6±0.4% n=5). In presence of 10 μM SKF96365, a non selective Ca 2+ channels blocker, contractions induced by NH 4 Cl were reduced to 47.6±6.7% (n=7) as compared to the contractions induced by NH 4 Cl in the absence (100%) of SKF. On the other hand, in presence of 1 μM verapamil, a voltage operator Ca 2+ ‐channel blocker, and 0.05 μM calphostin C, a PKC inhibitor, contractions induced by NH 4 Cl were not altered. On isolated cells, SKF reduced the [Ca 2+ ]c to 72.2±1.7% (n=4). In conclusion, Ca 2+ influx through non selective Ca 2+ channels sensitive to SKF is important for the contractile response induced by NH 4 Cl in the rat anococcygeus muscle. Supported by FAPESP and CNPq.