Table 6.

Contractions and relaxations of the muscle in adult (35–60 years of age) and elderly (≥70 years) human ascending and descending colon

	Ascending		Descending
	Adult	Elderly	Adult	Elderly
Compounds causing muscle contraction*
Carbachol  0.001–10 µM	pEC50=6.5±0.5 Emax=50±10 g/g n=7	pEC50=6.2±0.3 Emax=43±6 g/g n=8	pEC50=6.4±0.2 Emax=53±5 g/g n=7	pEC50=7.0±0.4 Emax=45±6 g/g n=12
Bay-K8644 1 µM  (in presence of L-NAME 300 µM)	16±7 g/g n=5	17±8 g/g n=5	25±9 g/g n=5	13±3 g/g n=5
Compound causing muscle relaxation
SNP†  0.01–1000 µM	pEC50=6.5±0.8 Emax=1.7±0.2 g/g n=7	pEC50=6.4±0.6 Emax=1.9±0.2 g/g n=10	‡	‡

Data are expressed as mean±SEM muscle tension/g of tissue (when using the single concentration of Bay-K8644) or when concentration–response curves were constructed, as the pEC₅₀ and E_max values derived from these curves (see online supplementary file 3 for carbachol concentration–response curves in female/male, adult/elderly ascending and descending colon). There were no statistically significant differences between values obtained using adult ascending and descending colon or when these values were compared with the elderly (p>0.10 each).

*For comparison, in adult ascending and descending colon in the presence of L-NAME 300 µM, EFS generated, respectively, 4.1±1.1 and 2.1±0.5 g tension/g, approximately equivalent to the contraction evoked by, respectively, 60 and 4 nM carbachol (~EC₇ and EC₄ values).

†The effects of SNP were uninfluenced by breakdown in the presence of haemoglobin to form cyanide and methaemoglobin in addition to NO (each can affect tissue viability)—thus, the magnitude of relaxation evoked by SNP 100 µM in ascending colon was not different to that evoked by the NO donor, diethylamine NONOate 10 µM (respectively, 1.3±0.5 and 1.4±0.4 g/g, n=6 each, p>0.8).

‡Consistent, concentration-dependent relaxations could not be obtained in descending colon.

EFS, electrical field stimulation; L-NAME, N_ω -nitro-L-arginine methyl ester hydrochloride; NO, nitric oxide; SNP, sodium nitroprusside.