Aging and muscle fiber type alter K+ channel contributions to the myogenic response in skeletal muscle arterioles

Kang LS, Kim SJ, Dominguez JM 2nd, Sindler AL, Dick GM, Muller-Delp JM. Aging and muscle fiber type alter K+ channel contributions to the myogenic response in skeletal muscle arterioles. J Appl Physiol 107: 389-398, 2009. First published April 30, 2009; doi: 10.1152/japplphysiol.91245.2008.-Aging diminishes myogenic tone in arterioles from skeletal muscle. Recent evidence indicates that both large-conductance Ca2+-activated (BKCa) and voltage-dependent (K-V) K+ channels mediate negative feedback control of the myogenic response. Thus we tested the hypothesis that aging increases the contributions of K-V and BKCa channels to myogenic regulation of vascular tone. Because myogenic responsiveness differs between oxidative and glycolytic muscles, we predicted that K-V and BKCa channel contributions to myogenic responsiveness vary with fiber type. Myogenic responses of first-order arterioles from the gastrocnemius and soleus muscles of 4- and 24-mo-old Fischer 344 rats were evaluated in the presence and absence of 4- aminopyridine (5 mM) or iberiotoxin (30 nM), inhibitors of K-V and BKCa, respectively. 4- Aminopyridine enhanced myogenic tone with aging and normalized age-related differences in both muscle types. By contrast, iberiotoxin eliminated age-related differences in soleus arterioles and had no effect in gastrocnemius vessels. K(V)1.5 is an integral component of K-V channels in vascular smooth muscle; therefore, we determined the relative protein expression of K(V)1.5, as well as BKCa, in soleus and gastrocnemius arterioles. Immunoblot analysis revealed no differences in K(V)1.5 protein with aging or between variant fiber types, whereas BKCa protein levels declined with age in arterioles from both muscle groups. Collectively, these results suggest that the contribution of BKCa to myogenic regulation of vascular tone changes with age in soleus muscle arterioles, whereas increased K-V channel expression and negative feedback regulation of myogenic tone increases with advancing age in arterioles from both oxidative and glycolytic muscles.