Figure 2. Contraction and relaxation in intestinal smooth muscle. Original recordings of a colon (A–C) and jejunum (D--F) smooth muscle from a CTR (A, D) and Ca_v1.2^SMACKO mouse (B, E). Lines indicate the presence of 10 µM carbachol (CCh). C, F) Magnitudes of carbachol-induced tension in colon (C) and jejunum (F). In colon (A--C), the carbachol-induced contraction consisted of a phasic and a tonic response. In jejunum, the carbachol-induced contraction consisted of at least 3 components (D--F): a fast component at 5–10 s, a slow response at 10–120 s, and a tonic response within 10 min. G–I) Relaxation of carbachol-induced tonus by isradipine and SKF96365. G, H) Original recordings of muscles from a CTR (G) and a Ca_v1.2^SMACKO (H) mouse. Lines indicate the presence of 10 µM carbachol (CCh), 1 µM isradipine (ISR), and 10 µM SKF96365 (SKF). I) Inhibition of CCh-induced contraction by 1 µM isradipine and 10 µM SKF96365. Bars represent means ± SEM (n=4, each). J–L) Relaxation by SKF96365 of Ca²⁺-re-entry-induced contraction in jejunum smooth muscle from CTR and Ca_v1.2^SMACKO mice. J, K) Original recordings of a jejunum muscle strip from a CTR (J) and a Ca_v1.2^SMACKO (K) mouse. Muscle strips were preincubated for 30–40 min in Ca²⁺-free buffer containing 1 mM EGTA to which 1 µM thapsigargin was added. Lines indicate the addition of 4 mM Ca²⁺, SKF96365, and Gd³⁺, respectively. Numbers indicate log[SKF96365] in M. 1 mM Gd³⁺ was used to induce maximal relaxation. L) Magnitude of contraction induced by Ca²⁺-re-entry. Bars represent means ± SEM. **P < 0.01.