Radiotracer flux methods have demonstrated the presence of dihydropyridine(DHP)-insensitive and DHP-sensitive components of phenylalkylamine(PAA)-sensitive 45Ca2+ uptake in cockroach (Periplaneta americana) nervous system and skeletal muscle membranes respectively. When microsac and proteoliposome preparations were incubated with 10 μM (±)-verapamil, control uptake (i.e. K+-stimulated 45Ca2+ uptake measured in the absence of drugs, taken as 100%) was reduced by ∼ 80–90% in all preparations. However, when these preparations were incubated with 10μM (±)-nitrendipine, almost complete block of 45Ca2+ uptake by cockroach skeletal muscle proteoliposomes was observed, but (±)-nitrendipine at the same concentration failed to inhibit > 50% of control uptake by either microsacs or proteoliposomes prepared from nervous tissue. These findings suggest that tissue-specific Ca2+ channels with distinct pharmacological properties are present in cockroach nerve and muscle. PAA- and DHP-sensitivity are well-documented pharmacological characteristics of vertebrate L-type Ca2+ channels, so the results of the present study indicate that Ca2+ channels with L-type properties are present in insect skeletal muscle. By contrast, the identification of PAA-sensitive/DHP-insensitive components of 45Ca2+ uptake in cockroach nervous system preparations suggests that this tissue contains Ca2+ channels that are pharmacologically distinct from vertebrate L-type Ca2+ channels.
Radiotracer flux methods have demonstrated the presence of dihydropyridine(DHP)-insensitive and DHP-sensitive components of phenylalkylamine(PAA)-sensitive 45Ca2+ uptake in cockroach (Periplaneta americana) nervous system and skeletal muscle membranes respectively. When microsac and proteoliposome preparations were incubated with 10 μM (±)-verapamil, control uptake (i.e. K+-stimulated 45Ca2+ uptake measured in the absence of drugs, taken as 100%) was reduced by ∼ 80–90% in all preparations. However, when these preparations were incubated with 10μM (±)-nitrendipine, almost complete block of 45Ca2+ uptake by cockroach skeletal muscle proteoliposomes was observed, but (±)-nitrendipine at the same concentration failed to inhibit > 50% of control uptake by either microsacs or proteoliposomes prepared from nervous tissue. These findings suggest that tissue-specific Ca2+ channels with distinct pharmacological properties are present in cockroach nerve and muscle. PAA- and DHP-sensitivity are well-documented pharmacological characteristics of vertebrate L-type Ca2+ channels, so the results of the present study indicate that Ca2+ channels with L-type properties are present in insect skeletal muscle. By contrast, the identification of PAA-sensitive/DHP-insensitive components of 45Ca2+ uptake in cockroach nervous system preparations suggests that this tissue contains Ca2+ channels that are pharmacologically distinct from vertebrate L-type Ca2+ channels.
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