Table 3.

Comparison of the properties of the noradrenaline-evoked I_cat obtained from spectral density functions and single spontaneous cation channel currents in the presence of various external divalent cations concentrations

	Single channel data							Spectral density analysis of whole-cell current
Divalent cation concentration	γ (pS)	Po	Oτ1 (ms)	Oτ2 (ms)	Bτ1 (ms)	Bτ2 (ms)	Frequency (bursts s−1)	γ (pS)	τ1† (ms)	τ2† (ms)
0 ${\text{Ca}}_{\text{o}}^{2+}$	12 ± 2 **	0.02 ± 0.01	0.7 ± 0.1*	3.9 ± 0.4*	3.9 ± 0.7	5.8 ± 1*	12 ± 3	11 ± 2	1.4 ± 0.1	11 ± 1
3 μm${\text{Ca}}_{\text{o}}^{2+}$	22 ± 2	0.11 ± 0.03 **	1.3 ± 0.3	17 ± 2.3 **	2.8 ± 0.4	43 ± 4 **	17 ± 4*	22 ± 2	1.2 ± 0.2	44 ± 3
100 μm${\text{Ca}}_{\text{o}}^{2+}$	26 ± 2	0.15 ± 0.03 **	1.1 ± 0.2	6.2 ± 1.1	2.9 ± 1.4	42 ± 9*	45 ± 8**	24 ± 2	1.6 ± 0.4	45 ± 4
1.5 mm${\text{Ca}}_{\text{o}}^{2+}$	23 ± 1	0.05 ± 0.02	1.2 ± 0.3	7.4 ± 0.2	3.1 ± 0.3	16 ± 1	14 ± 1	19 ± 2	1.6 ± 0.3	15 ± 1
1.5 mm${\text{Sr}}_{\text{o}}^{2+}$	25 ± 2	0.14 ± 0.04*	1.1 ± 0.2	6.0 ± 0.7	3.6 ± 0.4	30 ± 5*	19 ± 3	22 ± 1	1.5 ± 0.1	24 ± 2
1.5 mm${\text{Ba}}_{\text{o}}^{2+}$	22 ± 1	0.06 ± 0.02	1.0 ± 0.1	5.3 ± 0.8	3.7 ± 0.4	13 ± 2	19 ± 4	20 ± 1	1.8 ± 0.3	12 ± 1

^†These values were obtained from τ=½πf_c, where f_c is the corner frequency (Helliwell & Large, 1998; Albert et. al. 2001). All mean values are calculated from at least five patches.

^*P < 0.05

^**P < 0.01 compared to values in 1.5 mm ${\text{Ca}}_{\text{o}}^{2+}$.