Calcium channel binding in nerves and muscle of canine small intestine
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Using [3H]-nitrendipine (Nit) and [125I]-omega conotoxin (w-CTX), the cellular and subcellular distribution of calcium channel subtypes in the homogenates of canine small intestinal circular muscle was studied. Nit. bound to the membranes from the circular smooth muscle cells (PM) and to the synaptosomal membranes from the deep muscular plexus (DMP); the Kd and Bmax values of Nit binding from these two sources were similar (Kd 0.4 +/- 0.16 nM and 0.77 +/- 0.24 nM; Bmax 206 +/- 22 and 192 +/- 39 fmol/mg of protein in DMP and PM respectively). w-CTX, however, bound only to the DMP (Kd 18.41 +/- 7.5 pM, Bmax 265 +/- 36 fmol/mg of protein). In DMP, nifedipine (10(-6) M) failed to interact with the binding of w-CTX; similarly, no modulation of Nit binding with unlabelled w-CTX (10(-7) M) could be detected. Therefore w-CTX and Nit binding sites represent two distinct, non-interactive and differentially distributed binding sites in canine small intestine.
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