β Subunit heterogeneity of L‐type Ca2+ channels in smooth muscle tissues

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Abstract
Various β subunit isoforms stabilize different gating properties of voltage‐gated L‐type Ca2+ channels. We therefore investigated the expression of Ca2+ channel β subunit isoforms in different smooth muscle types on the protein level by immunoblotting and immunoprecipitation employing β subunit‐selective sequence‐directed antibodies. From the four known β subunit isoforms only β2 and β3 were detected in porcine uterus, bovine trachea and bovine aorta membranes. Multiple immunoreactive β2 bands were detected in a tissue‐selective manner indicating structural heterogeneity of β2. Immunoprecipitation of (+)‐[3H]isradipine‐prelabeled channels revealed that β2 and β3 participate in Ca2+ channel formation in uterus and trachea, and β3 in aortic smooth muscle. We conclude that β2 and β3 subunits form L‐type Ca2+ channels in smooth muscle tissues. This subunit heterogeneity may be important to fine‐tune channel function.