1. C. The available blockers act primarily at voltage-gated calcium channels of the L type. The three prototypes, verapamil, nifedipine, and diltiazem, act at three discrete sites at this channel.

2. B. The other three drugs (dihydropyridines) are characterized by relatively selective vasodilator effects with little if any cardiac effects at doses employed clinically for hypertension or angina.

3. D. The vasodilatory effects of nifedipine are largely restricted to arteries (and consequently the after-load). It does not alter venous tone (and thus preload) significantly.

4. C. Since they are metabolized in the liver, hepatic cirrhosis can be expected to alter their half-life.

5. A. Skeletal muscles depend on the mobilization of intracellular stores of calcium for their contractile responses rather than transmembrane flux of calcium through the calcium channels. Therefore, skeletal muscle weakness is not likely to occur.

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