Effect of doxorubicin on calcium receptors of myocardial cells

Pharmacological Research. Vol. 21, Supplement 1,1989

87

EFFECT OF DOXORUBICIN ON CALCIUM RECEPTORS OF MYOCARDIAL CELLS E. Monti,

L.

Paracchini,

G. Perletti

tst. di Farmacologia, sez, Farmacologia Applicata, untv, di Milano Key words: Doxorubicin -

Calcium -

Previous investigations on Doxorubicin

(DXR)

in

slow channels - Protein kinase-C

the acute cardiotoxic effects induced by

mammals

showed

that

the

impairment

of

the

contractile force produced by ttle drug is related to the inhibition of the cellular calcium exchangeability, whereby the fast exchanging pool is mainly affected (1). the activity

of

This pharmacokinetic parameter is the sum of

numerous

enzymes and cellular

structures

(2);

the

identification of the action of DXR on the cellular calcium exchanges was tested on the Ca-ATPase and the sarcolemmal Na-Ca exchange, Which were found to be inhibited by DXR (3, 4). In the present investigation we studied the effect of DXR on different cellular calcium targets, namely

the

(CaM) and

sarcolemmal

voltage-operated

channels

(VOC),

Calmodulin

Protein Kinase-C (PKC).

voc-enr-cnec

preparations were obtained from rat heart, PKC was iso-

lated from rat brain, commerCial CaM was used. The effect of DXR on VOC and CaM was evaluated by binding experiments using 3H-PN-200.110 as a specific ligand for VOC and 14C-DXR for CaM.

The effect of DXR on PKC

activity was evaluated by using HI-histone or protamine as substrate. DXR (Farmitalia-C.Erba, Milano) was from 0.05 to 0.6 mM.

tested at concentrations ranging

Here we focus the r-esutts obtained at the

concentration 0.1 mM, Which is

Of pharmacological interest because it

inhibits the contractility of isolated atria and

suppresses the fast

exchanging calcium pool (1). DXR 0.1 mM inhibits the PN-200.110 binding to

VOC by

16.31.

(mean

of

2

determinations)

(Fig.

ta):

Kd is

affected, While Bmax drops from 62.31 to 45.97 fmol/mg protein. activity

of

PKC is

inhibited

1043-6618/89/2110087--02/$03.00/0

by

26.05±3.67

1.

(Fig.

lb);

this

not The value

© 1989 The Italian Pharmacological Society

88

Pharmacological Research. Vol. 21. Supplement 1. 1989

corresponds to the effect observed when the enzyme operates either with

a

substrate

phosphatidilserine

requ iring

or

in

it s

the

absence.

presence The

of

former

calcium effect

and

is

the

consequence of the reported DXR-phospholipid competition (5), however here we show that DXR also exerts a direct inhibition on PKC. 1b

10

~8000

70

~7000 0..

PN

6000 ~5000

,, <10 t( ........ :50

~

c:

PN+OXR

~40

~4000

~JO u 20

~3000 '0

;2000 ,g 1000

f

f

0'"-------t.s 0 .0::1 0.5

10 0

1

100 200

~~ DXR does not appear to bind specifically to CaM.

400

eoc

~~ Taken together, the

literature data and the results of this study show that a concentrat ion on

of DXR of pllarmacological interest develops a multi-site action myocardial

structures bited; in

receptors

controlling

liv ing

cells

involved

both

the

inf lux

inhibi t ion

in

calc ium

and

efflux

of

the

t r ans por t, of

inf lux

whereby

calcium are

pr-eqommates,

inhisince

DXR brings about a diminution of the fast exchangeable calcium pool. REFERENCES Villani F, Picc inini F, Merelli P, Favall i L. Influence Adriamyc in on calcium exchangeability in card iac muscle and modifications by ouabain. Biochem Pharmacol 1976; 27:965-967. 1)

of its

2) Exton JH. Mechanisms of action of calcium-mob ilizing agonists: some variations on a young theme. FASEB J 1966; 2:2670-6. Caroni P, Villani F, Carafoli E. The card iotoxic antibiotic 3) Doxorubicin inhibits the Na/Ca exchange of dog heart sarcolemmal vesicles. FEBS Lett 1961; 130:164-6. 4) Tomlinson CW, Grodin DV, Rabkin SW. Adriamyc in cardiomyopathy: impli c a t ions with mild imp air men t of left ventr icular function. Biochem Pharmacol 1965; 34 :4033-41. 5) Palavoor- ST, Stein ST , Hait WN. Inhibition of protein kinase-C by antineoplastic agents: implications for drug resistance. stccnem stocnvs Res Commun 1967; 146:716-25.