RESUMO
Three types of calcium channels have been identified voltage-sensitive, receptor operated [cardiac muscle and vascular smooth muscle] and stretch operated [in some blood vessels] channels. Using electrophysiological and pharmacological techniques, three different types of voltage-gated calcium channels have been identified, namely, L-type [for long lasting, large channels], T-type [for transient, tiny channels] and N-type [for neuronal, neither L nor T]. Many compounds are known to have a calcium channel inhibitory effect. Calcium antagonists, based on the specificity of inhibition of the slow calcium current, can be classified into three groups: Group A: for 90 to 100 percent inhibition of calcium influx without change in the sodium current [verapamil, diltiazem and the dihydropyridines]; Group B: for 50 to 70 percent inhibition of calcium influx current without change in the sodium current [bepridil, cinnarizine and prenylamine] and Group C: for agents exhibiting some inhibition of calcium influx [phenytoin, indomethacin and propranolol]. There is now increasing evidence that, certain calcium channel blockers especially the dihydropyridines are more strongly associated with vasodilation of afferent arterioles than of efferent arterioles and also with increase intraglomerular pressure and albuminuria. Thus they have a beneficial effect in terms of reducing proteinuria and slowing the progression of diabetic renal failure