Changes in potassium balance: inverse relationship between number and affinity of angiotensin II receptors of smooth muscle and adrenal target tissues

¹ Department of Medicine, University Hospitals, Case Western Reserve University, Cleveland, Ohio 44106

Short-term administration of a high potassium diet to rats resulted in reciprocal changes in affinity and number of angiotensin II receptors of adrenal and smooth muscle target tissues as determined by a radioreceptor assay system. The changes consisted of an increase in mean equilibrium association constant (K_a) of smooth muscle receptor of 39%, from 0.23 ± 0.02 in controls to 0.32 ± 0.03 nM^–1 with high K⁺ diet. A decrease in adrenal receptor affinity of 28% occurred as a result of a decrease in mean K_a, from 0.9 ± 0.04 in controls to 0.65 ± 0.1 nM^–1 with K⁺ loading. The number of smooth muscle receptors for angiotensin II decreased by 42%, and the adrenal receptors increased by 122%. Potassium loading also affected the pressor and steroidogenic responses to angiotensin II. There was an enhanced pressor response to angiotensin II infused into nephrectomized anesthetized rats. The pattern of aldosterone response was more complex and consisted of a less sensitive aldosterone response to angiotensin II but a greater increment above control at high concentrations in isolated adrenal glomerulosa cells. It is possible that the increment in smooth muscle receptor affinity might have mediated the enhanced pressor responsiveness to angiotensin II, while the decrement in adrenal receptor affkity might have contributed to the less sensitive aldosterone response to angiotensin II. These studies emphasize the complexity of receptor alterations that are associated with altered hormonal responses in angiotensin target tissues and document that changes in potassium balance are important modulators.

Submitted on November 20, 1978
Accepted on June 22, 1979