M. Neusser et al., ANGIOTENSIN-II RESPONSES AFTER PROTEIN-KINASE-C ACTIVATION IN VASCULAR SMOOTH-MUSCLE CELLS OF SPONTANEOUSLY HYPERTENSIVE RATS, Journal of cardiovascular pharmacology, 21(5), 1993, pp. 749-753
To examine the interaction of protein kinase C (PKC) with agonist-indu
ced calcium fluxes in hypertension, cytosolic free calcium ([Ca2+]i) w
as measured in vascular smooth muscle cells (vSMC) of normotensive and
spontaneously hyper-tensive rats (SHR) after incubation with phorbol,
-12 myristate,-13 acetate (PMA) and application of angiotensin II (AII
). To distinguish between calcium influx through voltage-dependent cal
cium channels and calcium mobilization from intracellular stores, the
calcium agonist BayK 8644 was used. Resting [Ca2+]i was 108.0 +/- 10.6
nM (mean +/- SEM, n = 25) in normotensive and 102.0 +/- 11.4 nM (n =
21) in hypertensive cells. After pretreatment with PMA 10(-7) M for 60
min, resting [Ca2+]i of normotensive vSMC increased to 145.0 +/- 13.8
nM (n = 17) while the resting level of the hyper-tensive cells decrea
sed to 68.0 +/- 2.4 nM (n = 14, p < 0.05 as compared with normotensive
cells) in hypertensive vSMC. Maximum increase in [Ca2+]i induced with
10 M AII for normotensive and hypertensive vSMC was similar: 230.5 +/
- 34.4 nM (n = 14) and 212.5 +/- 26.7 nM (n = 17). After pretreatment
with PMA 10(-7) M, the maximum increase in [Ca2+]i induced by AII in h
ypertensive cells was limited to 108.0 +/- 6.2 nM (p < 0.05 as compare
d with normotensive cells), whereas the increase in [Ca2+]i in normote
nsive vSMC remained the same as before: 211.5 +/- 23.4 nM. After admin
istration of 10(-5) M BayK 8644, [Ca2+]i increased by 54.3 +/- 12.2 nM
(n = 4) and 43.4 +/- 17.4 nM (n = 5) in normotensive and hypertensive
vSMC, respectively. After preincubation with PMA this effect was redu
ced to 20.3 +/- 8.8 nM in normotensive cells and 29.0 +/- 4.6 nM in hy
pertensive cells. We conclude that in hypertensive vSMC either the fee
dback inhibition of postreceptor signaling after PKC activation is mor
e pronounced or that higher amounts of PKC can be activated.