The effect of calmodulin antagonists on amylase release from the rat parotid gland in vitro

The effect of several calmodulin antagonists on the release of alpha-amylase (EC 3.2.1.1) from rat parotid gland minces was investigated as an approach to determine whether calmodulin has a role in the stimulus-secretion coupling mechanism in this tissue. The phenothiazines, trifluoperazine, chlorpromazine, and thioridazine, failed to inhibit amylase release induced by N6,O2'-dibutyryl adenosine 3':5'-cyclic monophosphate. All three phenothiazines increased basal amylase release at high concentrations. This release was independent of cellular energy, indicating that the release was probably due to the membrane perturbing properties of these compounds rather than their ability to antagonize calmodulin. R24571, a more potent calmodulin antagonist, also failed to inhibit amylase release induced by N6,O2'-dibutyryl adenosine 3':5'-cyclic monophosphate but increased basal amylase release. A different calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, partially inhibited release while 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) completely blocked the amylase release induced by the cyclic AMP derivative. However, concentrations of TMB-8 inhibiting amylase release drastically reduced the ATP concentration of rat parotid minces, suggesting that the inhibition of secretion was due to toxic effects of TMB-8 on parotid cells rather than the ability of the compound to antagonize calmodulin. The use of calmodulin antagonists has therefore failed to implicate calmodulin as an intermediate in the stimulus-secretion coupling mechanism of the rat parotid gland.