Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of miRNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility.

A delayed rectifier voltage-gated K+ channel (Kv) represents the largest ionic conductance of platelets and megakaryocytes, but is undefined at the molecular level. Quantitative RT-PCR of all known Kv α and ancillary subunits showed that only Kv1.3 (KCNA3) is substantially expressed in human platelets. Furthermore, megakaryocytes from Kv1.3−/− mice or from wild-type mice exposed to the Kv1.3 blocker margatoxin completely lacked Kv currents and displayed substantially depolarised resting membrane potentials. In human platelets, margatoxin reduced the P2X1- and thromboxaneA2 receptor-evoked [Ca2+]i increases and delayed the onset of store-operated Ca2+ influx. Megakaryocyte development was normal in Kv1.3−/− mice, but the platelet count was increased, consistent with a role of Kv1.3 in apoptosis or decreased platelet activation. We conclude that Kv1.3 forms the Kv channel of the platelet and megakaryocyte, which sets the resting membrane potential, regulates agonist-evoked Ca2+ increases and influences circulating platelet numbers.

Introduction Corpus cavernosum myocytes generate spontaneous tone that contributes to penile detumescence. It is essential to elucidate how tone is generated to fully understand the processes involved in erection. Tissue experiments have shown that blockers of voltage-dependent Ca2+ channels (VDCCs) reduce tone. However, there is also a widespread belief that these channels are poorly expressed in this tissue. Furthermore, it is unclear how VDCC would interact with recently described intracellular Ca2+ waves, which initiate contractions. Aims (i) To directly examine VDCC currents in freshly isolated corpus cavernosum myocytes; and (ii) to study the relationship between VDCC and intracellular Ca2+ waves. Main Outcome Measures VDCC and cytosolic Ca2+ were measured using patch clamp and confocal microscopy. Methods Male New Zealand white rabbits were euthanized and corpus cavernosum myocytes dispersed enzymatically for patch clamp recording and confocal Ca2+ imaging (using fluo-4AM). Results Isolated myocytes developed robust VDCC that could be separated into two components. One activated at −45 mV, reversed at +40 mV, inactivated with a V1/2 of −27 mV and was enhanced by Ba2+. This component was blocked with nifedipine, but not Ni2+ or mibefradil. The other component inactivated with a V1/2 of −87 mV, was unchanged in Ba2+, and was blocked by Ni2+ or mibefradil, but not nifedipine. Even though Ni2+ had no effect on intracellular Ca2+ waves, nifedipine blocked them, although localized Ca2+ events remained. Conclusions At least two VDCC are expressed in rabbit corpus cavernousum myocytes. One may be designated L-type Ca2+ current, whereas the other is a putative T-type current. The L-current facilitates conversion of local Ca2+ events into global Ca2+ waves, whereas the putative T-current plays little part in this process. These results provide a new basis for understanding the role of L-type Ca2+ current in generating detumescent tone in the corpus cavernosum.

The muscular layer of the uterus (myometrium) undergoes profound changes in global excitability prior to parturition. Here, a mathematical model of the myocyte network is developed to investigate the hypothesis that spatial heterogeneity is essential to the transition from local to global excitation which the myometrium undergoes just prior to birth. Each myometrial smooth muscle cell is represented by an element with FitzHugh-Nagumo dynamics. The cells are coupled through resistors that represent gap junctions. Spatial heterogeneity is introduced by means of stochastic variation in coupling strengths, with parameters derived from physiological data. Numerical simulations indicate that even modest increases in the heterogeneity of the system can amplify the ability of locally applied stimuli to elicit global excitation. Moreover, in networks driven by a pacemaker cell, global oscillations of excitation are impeded in fully connected and strongly coupled networks. The ability of a locally stimulated cell or pacemaker cell to excite the network is shown to be strongly dependent on the local spatial correlation structure of the couplings. In summary, spatial heterogeneity is a key factor in enhancing and modulating global excitability.