Related Experiment Videos
Consequences of metabolic inhibition in smooth muscle isolated from guinea-pig stomach
S Nakayama1, S Chihara, J F Clark
1Department of Physiology, School of Medicine, Nagoya University, Japan. h44673a@nucc.cc.nagoya-u.ac.jp
Abstract:
1. In smooth muscle isolated from the guinea-pig stomach, cyanide (CN) and iodoacetic acid (IAA) were applied to block oxidative phosphorylation and glycolysis, respectively. Effects of IAA on generation of spontaneous mechanical and electrical activities were systematically investigated by comparing those of CN. Spontaneous activity ceased in 10-20 min during applications of 1 mM IAA. On the other hand, application of 1 mM CN also reduced the spontaneous activity, but never terminated it. In the presence of CN the negativity of the resting membrane potential was slightly reduced. 2. When spontaneous activity ceased with IAA, the resting membrane potential was not significantly affected. Also, before ceasing, the amplitude and duration of the spontaneous electrical activity were significantly reduced. The amplitude of the electrotonic potential was, however, not changed by IAA. Further, glibenclamide did not prevent the effects of IAA. These results suggest that, unlike cardiac muscle, activation of metabolism-dependent K+ channels in stomach smooth muscle does not seem to play a major role in reducing and terminating spontaneous activity during metabolic inhibition. 3. Carbachol-induced contraction transiently increased, and subsequently decreased gradually during application of IAA. 4. After 50 min application of IAA, when there was no spontaneous activity, the concentrations of phosphocreatine (PCr) and ATP measured with 31P nuclear magnetic resonance decreased to 60 and 80% of the control, respectively, while inorganic phosphate (Pi) concentration paradoxically fell to below detectable levels. During subsequent prolonged application of IAA, high-energy phosphates steadily decreased. On the other hand, after 50 min CN application, [PCr] and [ATP] decreased to approximately 30 and 80% of the control, respectively, while [Pi] increased by 2.6-fold. 5. In the presence of either CN or IAA, spontaneous mechanical and electrical activities were reduced or eliminated, although amounts of high-energy phosphates sufficient to contract smooth muscle remained. It can be postulated that some mechanism(s) related to energy metabolism, but not including ATP-sensitive K+ channels, plays an important role in generating spontaneous activity in guinea-pig stomach smooth muscle. During metabolic inhibition the energy metabolism-dependent mechanism(s) would preserve high-energy phosphates, and consequently cell viability, by stopping spontaneous activity.
Insights
Metabolic inhibition using iodoacetic acid (IAA) or cyanide (CN) reduced spontaneous activity in guinea-pig stomach smooth muscle. Energy metabolism, not ATP-sensitive K+ channels, appears crucial for this activity and cell viability during metabolic stress.
Area of Science:
- Physiology
- Biochemistry
- Smooth Muscle Biology
Background:
- Spontaneous activity in smooth muscle is vital for organ function.
- Energy metabolism significantly influences smooth muscle contractility and electrical activity.
- The role of specific metabolic pathways and ion channels in regulating stomach smooth muscle activity requires further elucidation.
Purpose of the Study:
- To investigate the effects of inhibiting glycolysis and oxidative phosphorylation on spontaneous activity in guinea-pig stomach smooth muscle.
- To compare the roles of glycolysis and oxidative phosphorylation in maintaining smooth muscle activity.
- To explore the involvement of ATP-sensitive K+ channels in metabolic inhibition-induced changes in smooth muscle activity.
Main Methods:
- Isolated guinea-pig stomach smooth muscle was treated with iodoacetic acid (IAA) to inhibit glycolysis and cyanide (CN) to inhibit oxidative phosphorylation.
- Spontaneous mechanical and electrical activities were recorded.
- Resting membrane potential, electrotonic potentials, and carbachol-induced contractions were measured.
- High-energy phosphate levels (ATP, phosphocreatine) and inorganic phosphate were quantified using 31P nuclear magnetic resonance.
Main Results:
- 1 mM IAA application led to the cessation of spontaneous activity within 10-20 minutes, while 1 mM CN reduced but did not terminate activity.
- IAA significantly reduced the amplitude and duration of spontaneous electrical activity without affecting the resting membrane potential or electrotonic potentials.
- Metabolic inhibition reduced high-energy phosphates, yet sufficient amounts remained for contraction, suggesting a non-contractile energy-dependent mechanism regulates spontaneous activity.
- Glibenclamide did not prevent IAA's effects, indicating ATP-sensitive K+ channels are not primarily involved.
Conclusions:
- Metabolic inhibition differentially affects spontaneous activity in stomach smooth muscle, with glycolysis inhibition being more potent in cessation.
- ATP-sensitive K+ channels do not appear to play a major role in regulating spontaneous activity during metabolic inhibition in this tissue.
- Energy metabolism-dependent mechanisms, distinct from ATP-sensitive K+ channels, are critical for generating spontaneous activity and preserving cell viability during metabolic stress in guinea-pig stomach smooth muscle.