Table 1.

Distribution of myosin heavy chain (MHC) isoforms in selected oral (digastric, masseter) and nasal (levator) muscles in rats exposed to an early episode of forced oral breathing (CN group) and in control rats [74]. The different MHC isoforms were characterized on PND 11 and 90 (for key to the functions of the different MHC isoforms, see the text). Short-term nasal obstruction, that is forced oral breathing, leads to long-term orofacial muscle fibre adaptation. We observed increases in MHC neonatal and adult type I isoforms in muscles involved with oral breathing, digastric, and masseter, in CN group versus control on PND11. No changes were observed in the levator muscle involved with nasal breathing on PND 11. There are increases in MHC adult type IIb isoforms in muscle involved with oral breathing, masseter, and in muscle involved with nasal breathing, levator, in CN group versus control on PND 90. Values are given as percentages of total MHC and comparisons were then made using t-test with the Bonferroni correction.

MHC isoforms	emb	neo	I	IIa	IIx	IIb
On PND 11
CN group
Digastric	7	78∗	15∗	—	—	—
Masseter	9∗	91∗	—	—	—	—
Levator	14	86	—	—	—	—
Control group
Digastric	6	85	9	—	—	—
Masseter	13	87	—	—	—	—
Levator	14	86	—	—	—	—
On PND 90
CN group
Digastric	—	—	—	20∗	44∗	37
Masseter	—	—	—	—	42∗	58∗
Levator	—	—	—	18∗	25∗	57∗
Control group
Digastric	—	—	—	24	37	38
Masseter	—	—	—	—	48	52
Levator	—	—	—	1	31	68

^∗Significantly different from control group at t = −10.37 to 26.03, P < 0.03 to <0.001.