Mechanical and electrophysiological effects of thiopental on rat cardiac left ventricular papillary muscle  A. Descorps-Declère, M.P. Sauviat, K. Samii, Y. Lecarpentier  British Journal of Anaesthesia  Volume 86, Issue 1, Pages 103-109 (January 2001) DOI: 10.1093/bja/86.1.103 Copyright © 2001 British Journal of Anaesthesia Terms and Conditions

Fig 1 Mechanical parameters of contraction in LV rat papillary muscle. (a) muscle shortening length (L/Lmax) plotted against time; (b) muscle force plotted against time; (c) muscle shortening velocity plotted against time. Twitch 1 was loaded at Lmax with preload only. Twitch 2 was loaded with the same preload as that of twitch 1 and abruptly clamped to zero-load with critical damping just after the electrical stimulus. Twitch 3 was fully isometric. The following parameters of contraction were measured: Vmax (maximum velocity at zero-load), ΔL (maximum shortening of the muscle at preload only, TPS (time to peak shortening of the isotonic twitch with preload only), +DF (positive derivative of isometric contraction), AF (maximum isometric active force), TPF (time to peak force of the isometric twitch). L (muscle length) and Lmax (initial muscle length at peak active tension). The shortening length was expressed as the ratio L/Lmax. In (c), the arrow represents the series element recoil; damping was adjusted to obtain a single oscillation. British Journal of Anaesthesia 2001 86, 103-109DOI: (10.1093/bja/86.1.103) Copyright © 2001 British Journal of Anaesthesia Terms and Conditions

Fig 2 Effects of application of thiopental (3.8×10−5 M) for 45 min on mechanical parameters of contraction of rat papillary muscle recorded in Krebs–Henseleit solution (control); (a) muscle shortening length (L/Lmax) plotted against time. (b) Muscle force plotted against time. (c) Shortening velocity plotted against time. Twitch 1 was loaded at Lmax with preload only; twitch 2 was loaded with the same preload as twitch 1 and clamped to zero load just after the stimulus; twitch 3 was fully isometric at Lmax. British Journal of Anaesthesia 2001 86, 103-109DOI: (10.1093/bja/86.1.103) Copyright © 2001 British Journal of Anaesthesia Terms and Conditions

Fig 3 Effect of thiopental on the action potential (AP) of rat LV papillary muscle recorded in Krebs–Henseleit control solution at a frequency of 0.2 Hz, using intracellular microelectrodes. (a) AP traces recorded on the same papillary muscle. (b) Histogram showing the effect of 3.8×10−6 M and 3.8×10−5 M thiopental on the AP parameters. Mean±sd of m impalements recorded from n muscles. control: m=20, n=8; thiopental 3.8×10−6 M: m=12, n=4; thiopental 3.8×10−5 M: m=16, n=6. Student's t-test for paired data:*P<0.05. RP, resting membrane potential; OS, overshoot; APD0, duration of the plateau measured at 0 mV; APD10, duration of the slow repolarizing phase of the AP measured at a membrane potential +10 mV higher than RP. British Journal of Anaesthesia 2001 86, 103-109DOI: (10.1093/bja/86.1.103) Copyright © 2001 British Journal of Anaesthesia Terms and Conditions

Fig 4 Effect of 1 mM 4-aminopyridine (4-AP) and 3.8×10−5 M thiopental on the action potential (AP) of rat papillary muscle recorded in Krebs–Henseleit solution, at a frequency of 0.2 Hz, using intracellular microelectrodes. (a) Top: dashed line, control solution; solid line, 4-AP; bottom: dashed line, 4-AP; solid line, control solution containing 4-AP and thiopental. (b) Histogram showing the effect of successive addition of 4-AP and thiopental in the control solution (empty bar) on the AP parameters. Mean±sd of m impalements recorded from n muscles. Control: m=20, n=8; 4-AP: m=31, n=4; 4-AP + thiopental 3.8×10−5 M: m=30, n=4. Student's t-test for paired data: *P<0.05. RP, resting membrane potential; OS, overshoot; APD0, duration of the plateau measured at 0 mV; APD10, duration of the slow repolarizing phase of the AP measured at a membrane potential +10 mV higher than RP. British Journal of Anaesthesia 2001 86, 103-109DOI: (10.1093/bja/86.1.103) Copyright © 2001 British Journal of Anaesthesia Terms and Conditions