Tyrosine Kinase Involvement in Renal Arteriolar Constrictor Responses to Angiotensin II

Abstract

Abstract-Experiments were performed to test the hypothesis that tyrosine kinase activity contributes to renal arteriolar contractile responses to angiotensin (Ang) II. Rats were subjected to short-term enalaprilat treatment to decrease endogenous Ang II formation before tissue was harvested for experiments with the in vitro blood-perfused juxtamedullary nephron technique. Acute surgical papillectomy was used to avoid the indirect afferent arteriolar effect of Ang II that arises through increased tubuloglomerular feedback sensitivity. Arteriolar lumen diameter responses to 1 and 10 nmol/L Ang II were monitored by videomicroscopic methods before and during treatment with various tyrphostin compounds: 100 mol/L AG18 (broad-spectrum tyrosine kinase inhibitor), 100 nmol/L AG1478 (selective epidermal growth factor receptor tyrosine kinase inhibitor), or 100 mol/L AG9 (inactive analog). Baseline afferent arteriolar lumen diameter averaged 23.5Ϯ1.2 m and was not influenced by any tyrphostin. Ang II (10 nmol/L) decreased afferent diameter by 11.1Ϯ1.0 m under untreated conditions, a response that was not altered by AG9 but significantly blunted by AG18 (34Ϯ9% inhibition) or AG1478 (52Ϯ8% inhibition). AG18 did not suppress afferent arteriolar contractile responses to membrane depolarization (20 to 55 mmol/L K ϩ bath). Efferent arteriolar baseline diameter averaged 24.1Ϯ0.8 m and was unaltered by AG18 or AG1478; however, efferent diameter responses to 10 nmol/L Ang II were diminished 52Ϯ10% by AG18 and 51Ϯ13% by AG1478. These observations indicate that Ang II signaling in renal afferent and efferent arteriolar vascular smooth muscle is either mediated or modulated by tyrosine kinase activity, including that of the epidermal growth factor receptor tyrosine kinase.

Angiotensin II Triggers EGFR Tyrosine Kinase-Dependent Ca 2+ Influx in Afferent Arterioles

“…AG9, an inactive tyrphostin analog (IC 50 Ͼ1250 mol/L for EGFR tyrosine kinase), 27 failed to alter the [Ca 2ϩ ] i response to Ang II in the present study or the contractile response to Ang II in our previous study. 8 This observation is consistent with the idea that AG1478 suppresses the afferent arteriolar Ang II response through its ability to inhibit tyrosine kinase activity rather than through a nonspecific effect of tyrphostin compounds. Our observations extend to the renal microvascular level reports that tyrosine kinase inhibition attenuates Ang II-induced [Ca 2ϩ ] i and contraction responses in VSM cells from aorta or mesenteric artery.…”

“…17,18 Moreover, we recently reported that renal arteriolar contractile responses to Ang II are suppressed by inhibition of EGFR tyrosine kinase activity. 8 The present study explored the …”

“…26 AG1478 acts as a very potent and selective EGFR tyrosine kinase inhibitor (IC 50 ϭ3 nmol/L), influencing other tyrosine kinases only at much higher concentrations. 27 We have shown that tyrphostin inhibition of tyrosine kinase activity does not alter K ϩ -induced afferent arteriolar constriction, 8 arguing against the possibility that these compounds exert a direct effect on L-type Ca 2ϩ channels. 28 The other EGFR tyrosine kinase inhibitor used in the present study was DAPH, a nontyrphostin compound that interacts with the ATP binding site of the enzyme.…”

“…We recently reported that renal arteriolar contractile responses to Ang II are suppressed by inhibition of EGFR tyrosine kinase activity 8 ; however, the mechanism underlying the EGFR involvement in this critical microvascular contractile response to Ang II remains unclear. Two possible mechanisms might be involved in this process.…”

Reduced alpha adrenergic mediated contraction of renal preglomerular blood vessels as a function of gender and aging

“…Vanadate-induced smooth muscle contraction (ileum) involves decreased activity of TyrP [Swarup et al, 1982] suggesting that TyrP activity modulates increased or decreased contractile activity of smooth muscle [Saifeddine et al, 1994]. In experiments in which angiotensin II was used to constrict the blood perfused afferent and efferent arterioles of juxtamedullary nephrons in young adult rats, broad spectrum blockade of TyrK reduced the constriction of those arterioles by 34% and 52%, respectively, demonstrating that reduction in TyrK activity reduces renal vascular constriction [Carmines et al, 2001]. When a TyrK inhibitor (AG1478) that specifically blocks the epidermal growth factor receptor (EGFR) TyrK was administered, the constriction to Angiotensin II in afferent and efferent arterioles was reduced 52% and 51%, respectively, suggesting that renal afferent arteriolar constriction to angiotensin II is most affected by the EGFR form of TyrK.…”