Gender differences in ANG II levels and action on multiple K⁺current modulation pathways in diabetic rats

Abstract

Gender differences were studied in ventricular myocytes from insulin-deficient (Type 1) diabetic rats. Cells were obtained by enzymatic dispersion of hearts from control male and female rats and from rats made diabetic with streptozotocin (100 mg/kg) 7–14 days before experiments. ANG II content, measured by ELISA, was augmented in diabetic males but unaltered in diabetic females. In diabetic ovariectomized females, ANG II levels were augmented as in males. ANG II affects multiple cellular pathways including activation of protein kinase C (PKC) and several tyrosine kinases as well as inhibition of protein kinase A (PKA). The involvement of these pathways in modulating outward K+ currents was studied. Transient and sustained outward K+ currents were measured using the whole cell voltage-clamp method. In males, these currents are attenuated under diabetic conditions but are augmented by the ANG II-converting enzyme inhibitor quinapril. Activation of PKA by 8-bromo-cAMP enhanced both K+ currents in cells from diabetic males. The augmentation of these currents by quinapril was blocked when PKA inhibition was maintained with the Rp isomer of 3′,5′-cyclic monophosphorothioate. Inhibition of tyrosine kinases by genistein also augmented K+ currents in cells from diabetic males. Action potentials were abbreviated by 8-bromo-cAMP and genistein. However, both genistein and 8-bromo-cAMP had no effect on K+ currents in cells from diabetic females. In cells from ovariectomized diabetic females, 8-bromo-cAMP and genistein enhanced these K+ currents as in males. Inhibition of PKC augmented the transient and sustained K+ currents in cells from diabetic males and females. A contribution of non-ANG II-dependent activation of PKC is suggested. These results describe some of the mechanisms that may underlie gender-specific differences in the development of cardiac disease and arrhythmias.

Sex-dependent impairment of cardiac action potential conduction in type 1 diabetic rats

“…Estrogen has long been recognized as a suppressor of the RAS (11,25). Earlier work from our laboratory (43) showed that angiotensin II elevation is smaller in diabetic female hearts than in male hearts, concordant with the present results.…”

“…Earlier work from our laboratory showed that cardiac angiotensin II levels and oxidative stress are increased in diabetic male hearts (41, 43). These changes are reduced or absent in diabetic females (41)(42)(43). Earlier work from our laboratory also showed that in vivo treatment of male rats with an angiotensin-converting enzyme (ACE) inhibitor reduces or prevents diabetes-induced increase in angiotensin II and the resulting oxidative stress (41).…”

“…We also identified sex differences in K ϩ -current modulation (42), partly attributed to selective activation of the cardiac RAS. Selective activation results in lower cellular angiotensin II levels in diabetic female hearts compared with diabetic male hearts (43). Concordantly, cells from diabetic females show less oxidative stress (41).…”

Cardiomyocyte dysfunction in insulin-resistant rats: a female advantage

“…For example, streptozotocin-induced diabetes depresses the rate of ventricular pressure development and prolongs the contraction and relaxation phases to a greater degree in papillary muscles from males than in those from females [12,28]. Also, in type 1 diabetic rats, the ventricular myocyte action potential is prolonged, corresponding to a decline in peak potassium currents in males but not in females [29,30]. Similar attenuation of peak potassium currents in males but not females is seen in ventricular myocytes from the db/db mouse model of type 2 diabetes with obesity [31], although whole-heart function is impaired to a similar degree in both sexes [32].…”

Differential autocrine modulation of atrial and ventricular potassium currents and of oxidative stress in diabetic rats

“…Chronically elevated ANG II attenuates K ϩ currents (57) and enhances oxidative stress (25), an important feature of diabetes (13,14). The involvement of ANG II in K ϩ current attenuation was suggested both by direct measurements of ANG II elevation (10,11,44) and by the fact that inhibition of either the angiotensin-converting enzyme (ACE) or blockade of ANG II receptors leads to augmentation of attenuated K ϩ currents (35,39) and associated channel proteins (42,43). Furthermore, relief of ANG II-mediated oxidative stress also augments these currents (41,56).…”