TABLE I.

Composition of Internal Solutions

		Cs Glutamatea or K2SO4 b	CaT	[Ca2+]	MgT	[Mg2+]
		mM	mM	nM	mM	mM
Frog	Varied [Ca2+]	100	0.177	100	4.51	0.3
		100	0.304	200	4.51	0.3
		100	0.474	400	4.51	0.3
		100	0.659	800	4.51	0.3
	Varied [Mg2+]	100	0.177	100	4.96	0.4
		100	0.176	100	5.34	0.5
		100	0.174	100	6.24	0.8
		100	0.172	100	7.84	1.45
Rat	Varied [Ca2+]	80	0.178	100	9.80	2.0
		80	0.306	200	9.79	2.0
		80	0.403	300	9.78	2.0
		80	0.443	350	9.78	2.0
		80	0.479	400	9.78	2.0
	Varied [Mg2+]	80	0.189	100	3.99	0.2
		80	0.186	100	5.53	0.5
		80	0.183	100	7.13	1.0
		73	0.168	100	14.3	4.0
		60	0.146	100	25.2	10.0
		28	0.091	100	59.8	40.0

All internal solutions contained (in mM) HEPES or trismaleate (10), EGTA (1), phosphocreatine (5), ATP (5), glucose (10), dextran 8% and Fluo-4 (0.1). ATP was added as Mg salt up to 5 mM. When low Mg was required, the difference to 5 mM was replaced by the Na salt. pH was adjusted to 7 using CsOH, and osmolality to 265 mOsm/kg for frog or 320 mOsm/kg for rat, using cesium glutamate or potassium sulfate (for frog or rat) or water as needed.

^aFrog.

^bRat.