Calcium recruitment in renal vasculature: NE effects on blood flow and cytosolic calcium concentration.
This study provides new information about the relative importance of Ca2+ mobilization and entry in the renal vascular response to adrenoceptor activation. We measured renal blood flow (RBF) in Sprague-Dawley rats in vivo using electromagnetic flowmetry. We measured intracellular free Ca2+ concentration ([Ca2+]i) in isolated afferent arterioles utilizing ratiometric photometry of fura-2 fluorescence. Renal arterial injection of NE produced a transient decrease in RBF. The response was attenuated, in a dose-dependent manner, up to approximately 50% by nifedipine, an antagonist of L-type Ca2+ entry channels. Inhibition of Ca2+ mobilization by 3,4, 5-trimethoxybenzoic acid-8-(diethylamino)octyl ester (TMB-8) inhibited the renal vascular effects of NE in a dose-dependent manner, with maximal blockade of approximately 80%. No additional attenuation was observed when nifedipine and TMB-8 were administered together. In microdissected afferent arterioles, norepinephrine (NE; 10(-6) M) elicited an immediate square-shaped increase in [Ca2+]i, from 110 to 240 nM. This in vitro response was blocked by nifedipine (10(-6) M) and TMB-8 (10(-5) M) to a degree similar to that of the in vivo experiments. A nominally calcium-free solution blocked 80-90% of the [Ca2+]i response to NE. The increased [Ca2+]i elicited by depolarization with medium containing 50 mM KCl was totally blocked by nifedipine. In contrast, TMB-8 had no effect. Our results indicate that both Ca2+ entry and mobilization play important roles in the renal vascular Ca2+ and contractile response to adrenoceptor activation. The entry and mobilization mechanisms activated by NE may interact. That a calcium-free solution caused a larger inhibition of the NE effects on afferent arterioles than nifedipine suggests more than one Ca2+ entry pathway.
D000818:Animals; D001160:Arterioles / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D020746:Calcium Channels, L-Type; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000737:chemistry; D004533:Egtazic Acid / Q000494:pharmacology; D004574:Electromagnetic Fields; D005456:Fluorescent Dyes; D016257:Fura-2; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000187:drug effects*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D010738:Type C Phospholipases / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000494:pharmacology*