Table 1.

The membrane potential, [Ca²⁺]_i and tension responses to PGF (10⁻⁵ M) and the effect of nifedipine (10⁻⁶ M) on these responses in myometrium from guinea-pigs at mid- and late pregnancy

	Initial component of response		Sustained component of response
	Mid	Late	Mid	Late
Depolarization level (mV)
Control	−17 ± 1(21)	−20 ± 2(18)	−20 ± 1(21)	−22 ± 1(18)
Nifedipine	−20 ± 2(21)	−31 ± 2*†(18)	−22 ± 1(21)	−30 ± 2*†(18)
Cytoplasmic calcium (nM)
Control	879 ± 199(11)	989 ± 302(8)	298 ± 35(11)	178 ± 33*(8)
Nifedipine	367 ± 141†(11)	173 ± 28 †(8)	230 ± 32(11)	163 ± 36(8)
Tension (%)
Control	—	—	100	100
Nifedipine	—	—	84 ± 3(19)	35 ± 2*(9)

PGF evoked membrane depolarization, an increase in [Ca²⁺]_i and an increase in tension. Nifedipine decreased the initial transient increase in [Ca²⁺]_i at both stages of pregnancy. The blocker had little effect on the depolarization, the sustained rise in [Ca²⁺]_i or on tension at mid-pregnancy but markedly suppressed these parameters at late pregnancy. The number of tissues examined is given in parentheses.

^*Significantly different from mid-pregnancy.

^†Significantly different from control.