Neurohumoral changes in patients with left ventricular dysfunction following acute myocardial infarction and the effect of nitrate therapy: a randomized, double-blind, placebo-controlled long-term study

Diabetic neuropathy and heart failure: role of neuropeptides

Cardiovascular autonomic neuropathy (CAN), in which patients present with damage of autonomic nerve fibres, is one of the most common complications of diabetes. CAN leads to abnormalities in heart rate and vascular dynamics, which are features of diabetic heart failure. Dysregulated neurohormonal activation, an outcome of diabetic neuropathy, has a significant pathophysiological role in diabetes-associated cardiovascular disease. Key players in neurohormonal activation include cardioprotective neuropeptides and their receptors, such as substance P (SP), neuropeptide Y (NPY), calcitonin-gene-related peptide (CGRP), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). These neuropeptides are released from the peripheral or autonomic nervous system and have vasoactive properties. They are further implicated in cardiomyocyte hypertrophy, calcium homeostasis, ischaemia-induced angiogenesis, protein kinase C signalling and the renin-angiotensin-aldosterone system. Therefore, dysregulation of the expression of neuropeptides or activation of the neuropeptide signalling pathways can negatively affect cardiac homeostasis. Targeting neuropeptides and their signalling pathways might thus serve as new therapeutic interventions in the treatment of heart failure associated with diabetes. This review discusses how neuropeptide dysregulation in diabetes might affect cardiac functions that contribute to the development of heart failure.

Role of potassium channels in Dendroaspis natriuretic peptide-induced inhibition of gastric motility

AIM: To investigate the role of potassium channels in Dendroaspis natriuretic peptide (DNP)-induced relaxation of gastric antral circular smooth muscle of guinea pigs.

METHODS: The spontaneous contraction of gastric antral circular muscle of guinea pigs was recorded using a four-channel physiograph. The contents of cyclic guanosine monophosphate (cGMP) in gastric antral smooth muscle tissue and in perfusion medium were measured by radioimmunoassay. The whole cell patch-clamp technique was used to record calcium-activated potassium current (I_K(Ca)) and delayed rectifier potassium current (I_K(V)) in gastric myocytes isolated by collagenase digestion.

RESULTS: DNP inhibited the spontaneous contraction of gastric antral circular smooth muscle in a dose-dependent manner. DNP at concentrations of 1, 10, 100 and 1 000 nmol/L reduced the amplitude of the spontaneous contraction by 35% ± 6%, 54% ± 6%, 78% ± 13% and 94% ± 6%, respectively. LY83583, an inhibitor of soluble guanylate cyclase, significantly blocked DNP-induced relaxation of gastric antral circular smooth muscle (reduced amplitude: 42% ± 6% vs 60% ± 4%, P < 0.05). In contrast, zaprinast, a cGMP-sensitive phosphodiesterase inhibitor, potentiated DNP-induced relaxation of gastric antral circular smooth muscle (reduced amplitude: 72% ± 7% vs 58% ± 5%, P < 0.05). DNP markedly enhanced cGMP levels in gastric antral smooth muscle tissue and in perfusion medium. DNP increased the amplitude of I_K(Ca) at 60 mV by 62.31% ± 3.22%, but decreased the amplitude of I_K(V) at 60 mV by 18% ± 2.3% in gastric antral circular myocytes of guinea pigs.

CONCLUSION: DNP relaxes the gastric antral circular smooth muscle of guinea pigs by increasing IK(Ca) in a cGMP-dependent pathway. IK(V) may play a critical role in regulating resting membrane potential in gastric antral circular myocytes of guinea pigs.

Effects of dendroaspis natriuretic peptide on calcium-activated potassium current and its mechanism

In this study, we sought to investigate the effect of dendroaspis natriuretic peptide (DNP) on calcium-activated potassium current (I K(Ca)) and its mechanism in gastric antral circular smooth muscle cells (SMCs) using the whole-cell patch-clamp technique. DNP concentration-dependently increased macroscopic I K(Ca) and spontaneous transient outward currents (STOCs) in freshly isolated guinea pig gastric antral circular SMCs. The effects of DNP on I K(Ca) and/or STOCs were not blocked by applying calcium-free bath solution or the ryanodine receptor (RyR) antagonist ryanodine (10 microM), but they were inhibited by the inositol triphosphate receptor (IP3R) inhibitor heparin or the guanylate cyclase inhibitor LY83583. Moreover, a DNP-induced increase in STOCs was potentiated by the cyclic guanosine monophosphate (cGMP)-sensitive phosphoesterase inhibitor zaprinast. In conclusion, our results suggest that DNP increases I K(Ca) in gastric antral circular SMCs by increasing cGMP production and activating IP3Rs.

Inhibitory effect of dendroaspis natriuretic peptide on spontaneous contraction in gastric antral circular smooth muscles of guinea pigs

AIM

To determine whether the natriuretic peptide receptor (NPR) is present in the stomach of guinea pigs and to investigate the effect of dendroaspis natriuretic peptide (DNP) on the gastric motility of guinea pigs and its mechanism.

METHODS

The distribution of the NPR was analyzed by autoradioimmunography. The spontaneous contraction of gastric antral circular muscles of guinea pigs was recorded by a 4-channel physiograph. The whole cell patch-clamp technique was introduced to record calcium-activated potassium currents in the gastric myocytes isolated by collagenase.

RESULTS

The NPR existed in the gastric fundus, gastric body, and gastric antrum of guinea pigs, and its density was largest in the gastric antrum. DNP inhibited spontaneous contraction and exhibited a dose-dependent manner. The DNP-induced inhibition was diminished by LY83583 (a guanylate cyclase inhibitor) and was potentiated by zaprinast (a cGMP-sensitive phosphoesterase inhibitor). The inhibitory effect of DNP on spontaneous contraction was also inhibited by tetraethylammonium (a non-selective potassium channel blocker); 10 nmol/L DNP increased the calcium-activated potassium currents in the gastric circular myocytes of guinea pigs.

CONCLUSION

The NPR is most common in the gastric antrum of guinea pigs. DNP significantly inhibits gastric motility in the gastric antrum of guinea pigs. The inhibitory effect occurs via a cGMP-dependent pathway, and a calcium-activated potassium channel may be also involved in the relaxation induced by DNP in gastric antral circular smooth muscles.