K Whitely | PubMed Health

PubMed1997

Dissociated spatial patterning of gap junctions and cell adhesion junctions during postnatal differentiation of ventricular myocardium.

Nonuniformity in the spatial patterning of gap junctions between heart muscle cells is now recognized as an important determinant of electromechanical function in working myocardium. Breakdown of the normal geometry of electrical intercellular connectivity in diseased myocardium correlates with reentry, arrhythmia, and conduction disturbance. The developmental mechanism(s) that determines this precise spatial order in gap junction organization in normal myocardium is at present unknown. To examine this question, we have used immunoelectron and immunoconfocal microscopy to analyze the spatial distributions of gap junctional (connexin43), desmosomal (desmoplakin), and adherens junctional (N-cadherin) components during maturation of rodent and canine left ventricular myocardium. In rats, a striking divergence in the distribution of gap junctions and cell adhesion junctions emerged within the first 20 days of postnatal life. It was found that although gap junctions initially demonstrated dispersed distributions across myocyte cell membranes, desmosomes and adherens junctions showed more rapid polarization toward cell termini (ie, nascent intercalated disks) after birth. Over subsequent postnatal development (20 to 90 postnatal days), gap junctions became progressively concentrated in these cell adhesion junction-rich zones of membrane. Quantitative analyses of this process in a series of rats aged 15 embryonic and 1, 5, 10, 20, 40, 70, and 90 postnatal days indicated that significantly higher levels (P < .01) of N-cadherin and desmoplakin than of connexin43 were immunolocalized to cell termini by as early as postnatal day 5. Although all three junctions types showed increasing polarization to myocyte termini with development, variation between junctions remained significant (P < .05) at all times points between 5 and 70 postnatal days. Only at 90 postnatal days, when the animals were nearly full grown, did the proportions of gap junction, desmosome, and adherens junction at intercalated disks become statistically similar (P > .05). Examination of myocardium from 1- and 3-month-old canines revealed that related differential changes to the spatiotemporal distribution of intercellular junctions occurred during postnatal maturation of the dog heart, suggesting that the process was not rodent specific. It is concluded that this progressive change in the organization and pattern of association between gap junctions and cell adhesion junctions is likely to be an important factor in maturation of electromechanical function within the mammalian heart.

Animals↗

PubMed1987

Schistosoma mansoni: pH dependence of cercarial eicosanoid production, penetration, and transformation.

The pH dependence of Schistosoma mansoni cercarial penetration and transformation was determined using a gelatin:agar matrix, containing 3mM linoleate, as a penetration substrate. Penetration was largely unaffected by pH, approaching 100% over the pH range of 5.4 to 8.2, while transformation had an optimum pH range between 6.2 and 7.4. Within this pH range, between 74 and 89% of cercariae lost their tails. Outside this range, transformation decreased to 0% above pH 7.8 and dropped to 57% at pH 5.4. Esculetin, a lipoxygenase inhibitor, also incorporated into the agar:gelatin plates at a concentration of 1 mM, had little effect on cercarial penetration, except between pH 6.5 and 6.65, where penetration rates fell to 50% at pH 6.63. Transformation, however, was inhibited by esculetin, except between pH 6.5 and 6.8, where transformation was statistically equivalent to controls (P = 0.064, two-tailed Student's t test). Cercarial eicosanoid production measured at pH 6.55 and 7.2 in the presence and absence of 1 mM esculetin has led to the tentative identification of a 5-lipoxygenase product associated with cercarial penetration: LTB4 or 6-trans LTB4, a breakdown product of LTB4. We discuss the importance of pH control in cercarial experiments as well as the possible modulatory role skin pH (surface, epidermal, and dermal) may have in regulating cercarial eicosanoid production.

Agar↗