Figure 111

Differential activating mechanisms in afferent and efferent arterioles. The relative contributions of the activation pathways are different in afferent and efferent arterioles. Increases in cytosolic Ca2+ in afferent arterioles appear to be primarily by calcium ion (Ca2+) entry by way of receptor- and voltage-dependent Ca2+ channels. The efferent arterioles are less dependent on voltage-dependent Ca2+ channels. These differential mechanisms in the renal vasculature are exemplified by comparing the afferent and efferent arteriolar responses to angiotensin II before and after treatment with Ca2+ channel blockers. A, These experiments were done using the juxtamedullary nephron preparation that allows direct visualization of the renal microcirculation [21]. AA—afferent arteriole; ArA—arcuate artery; PC—peritubular capillaries; V—vein; VR—vasa recta.

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FIGURE 1-11 (Continued)

B, Both afferent and efferent arterioles constrict in response to angiotensin II [22]. Ca2+ channel blockers, dilate only the afferent arterioles and prevents the afferent vasoconstriction responses to angiotensin II. In contrast, Ca2+ channel blockers do not significantly vasodilate efferent arterioles and do not block the vasoconstrictor effects of angiotensin II. Thus, afferent and efferent arteri-oles can be differentially regulated by various hormones and paracrine agents. (Panel A from Casellas and Navar [21]; panel B from Navar et al. [23].)

Relaxing factors Constricting factors

Angiotensin II

Angiotensin II

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