DIMINISHED MYOFIBRILLAR SENSITIVITY TO CALCIUM PRODUCED BY SIMULTANEOUS SUPERFUSION OF CAMP AND PHOSPHODIESTERASES INHIBITORS IN TOAD (BUFO-ARENARUM-HENSEL) VENTRICLE
Mv. Petroff et A. Mattiazzi, DIMINISHED MYOFIBRILLAR SENSITIVITY TO CALCIUM PRODUCED BY SIMULTANEOUS SUPERFUSION OF CAMP AND PHOSPHODIESTERASES INHIBITORS IN TOAD (BUFO-ARENARUM-HENSEL) VENTRICLE, ARCH I PHYS, 101(5), 1993, pp. 279-283
Citations number
28
Categorie Soggetti
Physiology,Biology,Biophysics
Journal title
Archives internationales de physiologie, de biochimie et de biophysique
Experiments were performed in EGTA-skinned trabeculae from toad ventri
cle to explore the effects of the cAMP on calcium sensitivity of the c
ontractile system. 10(-3) M of the cAMP derivative dibutyryl cAMP (dcA
MP) failed to affect calcium sensitivity of chemically skinned ventric
ular trabeculae. 10(-5) M of the phosphodiesterase inhibitor isobutylm
ethylxantine (IBMX) produced a significant shift to the left of the te
nsion-pCa relationship. The computed half maximally activating pCa (pC
a50) were 6.32 +/- 0.03 and 6.40 +/- 0.01 in the absence and presence
of IBMX respectively, (P<0.05). Simultaneous perfusion of 10(-5) M IBM
X and 10(-3) M dcAMP suppressed the leftward shift of the tension-pCa
curve induced by IBMX (pCa50 : 6.33 +/- 0.04 and 6.33 +/- 0.05 for con
trol and IBMX respectively). Perfusion with the phosphodiesterase inhi
bitor milrinone (10(-5) M), did not produce any significant changes in
the tension-pCa relationship. Simultaneous perfusion of 10(-5) M milr
inone and 10(-3) M dcAMP significantly shifted to the right the tensio
n-pCa curve. The computed pCa50 were 6.32 +/- 0.02 and 6.23 +/- 0.03 u
nder control conditions and in the presence of dcAMP plus milrinone re
spectively (P < 0.05). In agreement with what has been described in ma
mmalian heart, the results indicate that in amphibian ventricle, cAMP
produced a decrease in the calcium sensitivity of the contractile prot
eins that is only evident in the presence of phosphodiesterase inhibit
ors. It is suggested that this decrease in myofilament sensitivity to
calcium may be one of the mechanisms by which beta-agonists enhance my
ocardial relaxation in the amphibian heart.